Numerous vehicles of the track or wheel type to perform various material handling operations have been proposed. One type of vehicle that recently has received a remarkable degree of attention is a small unit that incorporates four wheels which are driven by two separate power sources and the steering or turning movement is accomplished by driving the pair of wheels on one side of the vehicle in one direction while the second pair of wheels is either in a neutral condition or driven in the opposite direction. These vehicles have generally been referred to as skid steer vehicles.
One type of skid steer vehicle that is presently commerically available incorporates hydraulically actuated fluid translating devices as the power train between the engine and the respective pair of wheels. In order to simplify the construction and reduce the cost of the vehicles of this type, the actuation of the fluid translating devices is controlled through manual control levers that respectively cooperate with the two translating devices on opposite sides of the vehicle and the fluid translating devices are maintained in engagement by manual forces applied to the control levers.
In the past, it has been customary to interconnect the manual control levers and the respective fluid control devices through a mechanical linkage means. While the direct mechanical linkage connection provides a satisfactory interconnecting means between the control lever and the control arm on the fluid translating device, several problems are inherent with such an arrangement. One of the problems encountered is the fact that in small vehicles, particularly of the type under consideration, it is difficult to position the control levers in a position where they are readily accessible to the operator and still provide a simplified connection between the control lever and the arm. Usually, the areas in which the linkages must be located are very congested which makes it difficult to provide such mechanical connections. Furthermore, for safety reasons, it is essential that the control system automatically be returned to the neutral condition when the levers are released.
The mechanical linkage interconnection has an additional disadvantage in that the direct linkage connection results in considerable vibration and shock being transmitted to the control lever which is disagreeable to the operator and results in substantial wear of the various parts.
While various alternate types of interconnections have been proposed to be substituted for the linkage connection, these types of connections have not found any large degree of commercial success, particularly in the small vehicles of the type under consideration, primarily because of the expense and complexity for such systems.